The long term goals of this new program are an understanding of persistent viral infection and central nervous system (CNS) demyelinating disease. To this end, this program represents a multidisciplinary approach to defining mechanisms of viral persistence and myelin loss using a well defined murine model of demyelination induced by the neurotropic JHM strain (MHV-4) of mouse hepatitis virus (JHMV). This model provides a means to understand the interactions between a pathogen and its natural host that result in demyelination during acute and persistent CNS infection. The host response is competent to control infectious virus. However, a persistent CNS infection without detectable infectious virus is associated with chronic ongoing myelin loss. The pathological alterations within the CNS during viral persistence have numerous similarities to multiple sclerosis, the most prevalent human demyelinating disease. This program is unique, comprising a core of investigators addressing fundamental questions of viral persistence and immune responses, both as protective mechanisms and as inducers of demyelination. Project 1 focuses on the pro-inflammatory and anti-inflammatory effects of innate immunity. New data suggest that the limited capacity of oligodendroglia to respond to innate signals protect from oligodendroglial dysfunction and myelin loss. This project uses newly developed techniques and novel transgenic mice to demonstrate the unique response of oligodendroglia during both acute viral encephalomyelitis and viral persistence. Project 2 explores the unknown area of T cell retention and homeostasis within the CNS. The role of CNS resident and infiltrating cells in presenting viral antigen as well as the potential for cross priming are defined using a variety of transgenic and bone marrow chimeric mice. Project 3 analyzes the role of regulatory T cells and the anti-inflammatory cytokine IL-10 in CNS viral persistence and demyelination. This project uses a novel transgenic mouse which allows definition of the role of regulatory T cells during viral persistence and ongoing demyelination. Data obtained from these projects will provide novel insights into the mechanisms regulating viral persistence and demyelination as well as the CNS as a target for viral persistence. Importantly, it will provide valuable information on the interactions of specific CNS cells involved in viral persistence and demyelination and the cellular and soluble mediators of the host immune response.